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Trip Concept

thread830-206195

Trip Concept

Trip Concept

(OP)
Hello all,

Could anyone tell me if Safety PLCs are exclusively designed to operate using a de-energize-to-trip concept?

Most SIS systems are designed using a de-energize-to-trip concept. I tried, in vain, through IEC 61508/511 to see if I could find any paragraph or so dealing with the issue. Coul anyone also help me on that?

Thanks for your help.

Replies continue below

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RE: Trip Concept

It depends.

Fail safe design is normal for most process applications.  However, some of the NFPA standards such as deluge systems use supervised circuits and energize outputs to open deluge valves, etc.

RE: Trip Concept

No. Safety PLCs are not designed to use de-ernergise to trip or energise to trip.

A safety PLC needs to be designed and configured to do what is the "safe sate" in case of a shutdown.

De-energise to trip is not always the "safe" state. Each case is different.

"Do not worry about your problems with mathematics, I assure you mine are far greater."   
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RE: Trip Concept

(OP)
Thanks a lot guys!!!
Have a nice weekend.

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